1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus and, more particularly, to a high power cathode, which provides better uniformity in the material deposited, particularly in the area of semi-conductor manufacturing.
2. Description of Related Art
A typical magnetron sputtering device includes a vacuum chamber having an electrode contained therein, wherein the electrode includes a cathode portion, an anode portion and a target. The term electrode is oftentimes referred to in the industry as a cathode. In operation, a vacuum is drawn in the vacuum chamber followed by the introduction of a process gas into the chamber. Electrical power supplied to the electrode produces an electronic discharge which ionizes the process gas and produces charged gaseous ions from the atoms of the process gas. The ions are accelerated and retained within a magnetic field formed over the target, and are propelled toward the surface of the target which is composed of the material sought to be deposited on a substrate. Upon striking the target, the ions dislodge target atoms from the target which are then deposited upon the substrate. By varying the composition of the target, a wide variety of substances can be deposited on various substrates. The result is the formation of an ultra-pure thin film deposition of target material on the substrate.
FIG. 1 is a sectional side view of a prior art magnetron sputtering electrode 1 that includes a target 2 held in place by a clamping ring 4, which in turn, is affixed to a top of the cathode body 10 via a plurality of screws 6 and 8, respectively. The electrode 1 also includes a sealing plate 12, which forms a seal between the cathode body 10 and the sealing plate 12 via an O-ring 14. The water chamber 16 is defined between the cathode body 10 and the sealing plate 12 and includes a magnetic assembly comprising a magnetic field shaping ring 18, a plurality of magnets 20 and 22, a base ring 24 and a central magnet 26 centered within the magnetic field shaping ring 18. The magnets 20, 22 and 26 are generally standard magnets that can produce a residual flux density of about 38 MGO (Mega Gause Orstead). The electrode 1 further includes a water inlet supply 28 and a water outlet 30 for allowing cooling water to flow through the water chamber 16. The electrode 1 also includes a ring-shaped anode shield 32 that is affixed to an anode shield support 34 via a plurality of screws 36 and 38, respectively. The anode shield support 34 is affixed to a base plate 40 via a plurality of screws 42 and 44. An insulating plate 46 is interposed between base plate 40 and sealing plate 12, wherein the insulating plate 46 electrically insulates the cathode body 10 and the sealing plate 12 from the base plate 40. A water-tight seal is maintained between the insulating plate 46 and the sealing plate 12 by an O-ring 48 interposed therebetween. A power cable 50, which is affixed to the sealing plate 12 via a screw 52, supplies electric current to the cathode body 10 over the interface of the cathode body 10 with sealing plate 12 in the vicinity of O-ring 14.
There are several problems that exist with respect to prior art sputtering devices. Because the sputtering process produces intense heat, the power rating of the sputtering device is limited primarily by the ability to cool the device by means of flowing water. Overheating of the device due to inefficient cooling will cause stress cracks to form in highly stressed target materials, such as ceramic and brittle metals, which can cause arcing and short outs. This heat buildup causes higher electrical resistance, which impedes the flow of electrons thereby yielding lower deposition rates than would otherwise have been possible if such heat were not present. Further, because the prior art anode shield 32 is above the target surface level, buildup of target material occurs on a surface of the anode shield 32, which has a tendency to flake off and fall back onto the target 2 thus causing a short out.
In semi-conductor manufacturing, electrical components, for example, resistors, transistors, and capacitors, are commonly mounted on circuit panel structures, such as printed circuit boards. Circuit panels ordinarily include a generally flat sheet of dielectric material with electrical conductors disposed on a major, flat surface of the sheet, or on both major surfaces. The conductors are commonly formed from metallic materials, such as copper and serve to interconnect the electrical components mounted to the board. Where the conductors are disposed on both major surfaces of the panel, the panel may have via conductors extending through holes (or through vias) and the dielectric layer so as to interconnect the conductor on opposite surfaces. These vias can be on the order of sub-atomic sizes. Presently, prior art electrodes, such as electrode 1 shown in FIG. 1, can typically provide continuous discharge at power levels of 250 watts/in2 thus resulting in non-uniform coating C of a via V of a substrate S such as shown in FIG. 2.
Plasma density refers to the number of gaseous ions retained within the magnetic field. With an increase in plasma density, higher power such as in the range of 500-1000 watts/in2 can be supplied allowing for higher deposition rates. However, the typical prior art sputtering electrode 1 operating in a range of 500-1,000 watts/in2 can only be achieved through pulsing the electrode instead of a continuous discharge, or otherwise the electrode will quickly burn out. This pulsing of the electrode at power levels ranging from 500-1,000 watts/in2 also results in a non-uniform coating C of the via V of the substrate S as shown in FIG. 2.
It has been shown that a continuous pulse discharge at power levels in the range of 500-1,000 watts/in2 provide sputtering that is more orderly and straight resulting in a coating C of uniform thickness of a via V′ of a substrate S′ as shown in FIG. 7. Therefore, there is a need for a robust high power cathode (i.e., electrode) that has a more efficient cooling arrangement than that of the prior art electrode such that the cathode can provide continuous discharge at high power as opposed to a pulsing arrangement.